And coalescence around specific northbound and southbound APIs for application- and controller-to-switch interaction.

"We'll have QoS and security issues resolved" in OpenFlow 1.3 says Eric Johnson, CEO of Adara Networks, a Silicon Valley-based company that develops SDN software. "You'll see cloud controller software start to centralize around one version of OpenFlow. And then you'll also see northbound APIs and southbound APIs with greater use of Interface to Routing System (specifications) as well as OpenFlow."

Johnson believes RESTful APIs will be the standard on the northbound side while OpenFlow will be among several APIs used on the southbound side. In fact, one southbound API could be SNMP, he says, the network management polling protocol that's been in use for decades.

"There's a lot of legacy network infrastructure for which something else (besides OpenFlow) would be better, because you may not want to replace the control plane," Johnson says. "You may just want to leverage it."

Big Switch agrees with the need to be able to include legacy investments in SDN architectures and supports what it calls a hybrid approach to network virtualization, using both native OpenFlow and an overlay approach to support network resources that do not "sit on a hypervisor," says co-founder Kyle Forster.

Big Switch, one of the founding fathers of the SDN movement, had a big year in 2012, officially unveiling its OpenFlow-based controller and applications, disclosing a large roster of partners (including many industry heavy hitters), and announcing big customers - Fidelity Investments and Goldman Sachs. It also celebrated 10,000 downloads of Floodlight, the open source version of its SDN controller code.

What does it see on tap for 2013?

A doubling of the number of Floodlight downloads, for one, Forster says. Another expectation is that vendors that offer complete SDN solutions - data plane, control plane and applications, all inclusive - will start to separate themselves from the pack, based on customer demand.

"We'll see big Fortune 500s really lead the charge and say, 'Hey, here's the stuff that's mature enough for us to put into our networks,'" Forster says.

And while OpenFlow today has been focused on Layer 2/3 virtualization, Forster expects 2013 to usher in more players focused on Layer 4-7 applications and services, such as firewalls, application delivery controllers and monitoring in multitenant environments.

Cisco plans to roll out onePK on its three strategic operating systems - IOS, IOS XR and NX OS - meaning more Cisco products will become programmable in 2013. And with 70% to 80% market share in enterprise routing and switching, that means more users will be testing or implementing programmable networks next year.

"2013 is going to be huge for deployments," says David Ward, chief architect and CTO of Cisco's Service Provider division. "We have a lot in the pipeline that's going to come out" across our enterprise, data center, cloud, mobility and WAN service provider product lines.

Besides working to implement onePK across its operating systems, Cisco has been bulking up the orchestration capabilities of a programmable onePK environment, making a few acquisitions in 2012 to support that effort. The goal, Ward says, is to simplify IT operations for Cisco's varied customer sets.

OnePK helps accelerate network operations by providing a uniform interface across Cisco's three strategic operating systems. Then, service rollout becomes more flexible and agile, and compute, networking and storage resources become readily accessible and more accommodating.

Nicira, which was acquired by VMware last year for $1.2 billion, has been working with customers for two years to implement data center network virtualization. The company expects many more customers to publicly emerge in 2013, but as a prelude to more substantial evidence the following year.

"2013 will be the announcements and pre-announcements," says Martin Casado, CTO and co-founder of Nicira. "But in 2014, you'll really see the rubber hit the road. You'll see a more mature adoption curve."

So what might disrupt all of this momentum?

"I think we'll see a Balkanization where the traditional SDN interface will be more suited for research and educational type uses, and where applications like network virtualization are customer and product focused," Casado says. "I don't think there'll be anything to change the momentum from a high level - people want more flexible networks. But it's not going to be some big unified front like we're seeing now," he says. That's because vendors will start to customize their offerings in an attempt to distinguish their products.

Adara's Johnson believes any disruption to SDN's momentum will be market-driven, not technological.

"If anything derails SDN, it will be that it gets subsumed," he says. "Large vendors...may subsume all of the technological innovations to the point where the innovations really didn't come from [the developers]. When you incorporate it into a larger mix of platforms and provide a set of customizable capabilities, that may be enough to stop the innovation."

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